"We agree there should be a memorial day of some sort, but we don't believe that business should have to foot the bill for that solely."
She said she wanted to see some kind of one-off financial support from Government to businesses to help with the cost of the public holiday.
A suggestion to have the memorial day on a Sunday was a good one because fewer businesses would be disrupted, Garner said.
Whanganui mayor Hamish McDouall said the one-off public holiday would be appropriate.
"She gave service for 70 years ... I think it's ... appropriate to spend a day where actually everyone should consider how they can best serve the community."
He said it would be a good opportunity for workers to have a break but that there would also be some parents who would still have to work and would now need to find childcare.
Usual Holidays Act public holiday requirements will be in force.
The State Memorial Service will be held in the Wellington Cathedral of St Paul on the day of the public holiday, and will be televised and livestreamed.
"The decision to hold a one-off public holiday in the Queen's honour is also in line with similar holidays in the UK and Australia, and is in keeping with what is an historic event," Ardern said.
Ardern has also confirmed she will represent New Zealand, alongside the Governor-General, at the funeral of Queen Elizabeth II in London.